P1518 code, Symptoms no one else has
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From: Newark NY
P1518 code, Symptoms no one else has
Hey guys. A couple days ago my c5 cranked a very long time before starting, When it did start i got a reduced engine power message, Along with p1518 code and also a Service traction code ( i dont remember the exact code i cleared it) Anyway i was able to clear the code and start up and drive normal for about 2 days. Now today im getting ONLY the p1518 code. The car will not start AT ALL and i cannot clear the code. I have searched and searched and everyone that seems to have this code all say the car starts but wont drive. Im not looking to drop $300 on a new TAC to find out that isint the issue, What else could it be?
Things ive done
-Tried clearing code (worked the first time)
-Unhooked battery for 10 min to clear
-Unpluged and cleaned connections on TAC (they looked perfect)
Things ive done
-Tried clearing code (worked the first time)
-Unhooked battery for 10 min to clear
-Unpluged and cleaned connections on TAC (they looked perfect)
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From: Cape Coral, Florida
Hi !!
I remember a few weeks ago a gentlemen had the P1518 but the car would only idle but no throttle control. P1518 is very sensitive to battery voltage. How is your battery ??...have you had it like load tested recently ??...I’d do that first. Even with a P1518 the car will start but only idle...normally !!... Check fuse 17 (THROT CONT) in the underhood fuse box. Make sure you have at least feed voltage on one side of the fuse with KOEO...If NO voltage to either side might be a bad ignition relay (42)...If voltage to one side only turn OFF ignition...you should NOT have voltage to the THROT CONT fuse (17)...if so can be a short from the TAC module ignition feed circuit to battery voltage...you would check at TAC Module with TAC harness dis connected... !!...We can just start there...There is more to testing the TAC Module than just a visual inspection. Checking for shorts and opens on the harness may be in order. Also check the TAC motor wiring too...I don’t have a wiring diagram in front of me right now so I can’t be of more help !!...keep us advised !!
I remember a few weeks ago a gentlemen had the P1518 but the car would only idle but no throttle control. P1518 is very sensitive to battery voltage. How is your battery ??...have you had it like load tested recently ??...I’d do that first. Even with a P1518 the car will start but only idle...normally !!... Check fuse 17 (THROT CONT) in the underhood fuse box. Make sure you have at least feed voltage on one side of the fuse with KOEO...If NO voltage to either side might be a bad ignition relay (42)...If voltage to one side only turn OFF ignition...you should NOT have voltage to the THROT CONT fuse (17)...if so can be a short from the TAC module ignition feed circuit to battery voltage...you would check at TAC Module with TAC harness dis connected... !!...We can just start there...There is more to testing the TAC Module than just a visual inspection. Checking for shorts and opens on the harness may be in order. Also check the TAC motor wiring too...I don’t have a wiring diagram in front of me right now so I can’t be of more help !!...keep us advised !!
Last edited by C5 Diag; Sep 19, 2018 at 10:33 AM. Reason: add wiring diagram
Thread Starter
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Joined: Mar 2017
Posts: 62
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From: Newark NY
Hi !!
I remember a few weeks ago a gentlemen had the P1518 but the car would only idle but no throttle control. P1518 is very sensitive to battery voltage. How is your battery ??...have you had it like load tested recently ??...I’d do that first. Even with a P1518 the car will start but only idle...normally !!... Check fuse 17 (THROT CONT) in the underhood fuse box. Make sure you have at least feed voltage on one side of the fuse with KOEO...If NO voltage to either side might be a bad ignition relay (42)...If voltage to one side only turn OFF ignition...you should NOT have voltage to the THROT CONT fuse (17)...if so can be a short from the TAC module ignition feed circuit to battery voltage...you would check at TAC Module with TAC harness dis connected... !!...We can just start there...There is more to testing the TAC Module than just a visual inspection. Checking for shorts and opens on the harness may be in order. Also check the TAC motor wiring too...I don’t have a wiring diagram in front of me right now so I can’t be of more help !!...keep us advised !!
I remember a few weeks ago a gentlemen had the P1518 but the car would only idle but no throttle control. P1518 is very sensitive to battery voltage. How is your battery ??...have you had it like load tested recently ??...I’d do that first. Even with a P1518 the car will start but only idle...normally !!... Check fuse 17 (THROT CONT) in the underhood fuse box. Make sure you have at least feed voltage on one side of the fuse with KOEO...If NO voltage to either side might be a bad ignition relay (42)...If voltage to one side only turn OFF ignition...you should NOT have voltage to the THROT CONT fuse (17)...if so can be a short from the TAC module ignition feed circuit to battery voltage...you would check at TAC Module with TAC harness dis connected... !!...We can just start there...There is more to testing the TAC Module than just a visual inspection. Checking for shorts and opens on the harness may be in order. Also check the TAC motor wiring too...I don’t have a wiring diagram in front of me right now so I can’t be of more help !!...keep us advised !!
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From: Newark NY
i have read all i could find. And like i said everywhere i saw people said there car still started just did not drive because of no response from throttle. This isint the issue im having
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From: Newark NY
Lastnight i went through everything i could. i pulled the battery again, I unplugged and plugged everything on the TB, and the TAC itsself. I unplugged all the ground points in the engine bay and cleaned and reinstalled along with unbolting, sanding, And rebolting them back. I Even inspected the wires above the TAC (below the battery) for any issues. Nothing!, put the battery back in and there has not been an issue in the 3 times ive driven it between lastnight and today. So maybe it was just a bad ground? ill keep posted if it happens again
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From: Cape Coral, Florida
This DTC's diagnostic is pretty involved as far as looking for shorts, opens, and resistance in the circuits in the TAC motor, TAC module, and PCM...it is NOT always a ground issue....if good it's basically it's going to come down to replacing the TAC Module OR PCM....why was the battery changed 4 months ago ??....these cars are real finicky as far as low battery voltage goes...just barely OK for starting but can throw these crazy DTC's !!!...like I had said it's rare that this DTC is not allowing the car to at least start...usually will start but no throttle response. Too bad you didn't live in Newark NJ instead of NY...you'd be 30 minutes away...LOL !!!
Last edited by C5 Diag; Sep 19, 2018 at 05:04 PM.
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From: Newark NY
So, a couple days later here i am again. Car ran fine all this time, parked it at work for 15 min. Come out to "reduced power" message and the code is back. Along with the TCS light, and code C1278. Which im reading the two codes go together? So im guessing either the PCM or TAC is bad? I don't have am issue replacing either. Just don't want to throw the money at it to not fix the issue.... Are there tests i can do? Or a shop can do to rule one or the other being bad?
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Thread Starter
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Joined: Mar 2017
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From: Newark NY
Sir,
This DTC's diagnostic is pretty involved as far as looking for shorts, opens, and resistance in the circuits in the TAC motor, TAC module, and PCM...it is NOT always a ground issue....if good it's basically it's going to come down to replacing the TAC Module OR PCM....why was the battery changed 4 months ago ??....these cars are real finicky as far as low battery voltage goes...just barely OK for starting but can throw these crazy DTC's !!!...like I had said it's rare that this DTC is not allowing the car to at least start...usually will start but no throttle response. Too bad you didn't live in Newark NJ instead of NY...you'd be 30 minutes away...LOL !!!
This DTC's diagnostic is pretty involved as far as looking for shorts, opens, and resistance in the circuits in the TAC motor, TAC module, and PCM...it is NOT always a ground issue....if good it's basically it's going to come down to replacing the TAC Module OR PCM....why was the battery changed 4 months ago ??....these cars are real finicky as far as low battery voltage goes...just barely OK for starting but can throw these crazy DTC's !!!...like I had said it's rare that this DTC is not allowing the car to at least start...usually will start but no throttle response. Too bad you didn't live in Newark NJ instead of NY...you'd be 30 minutes away...LOL !!!
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From: Cape Coral, Florida
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From: Cape Coral, Florida
MMMM ??...we can try to attack this as maybe just a normal "cranking no start" for now...correct that it DOES CRANK ??...I think the C1278 is a steering DTC...can't remember...now reading your initial post you said you had a "long crank time" when starting....this "symptom" sometimes points to a crank sensor going bad...did you have a longer crank time again ???...if you want we can attack this as I had said...a cranking no start. Let me know !!
Last edited by C5 Diag; Sep 25, 2018 at 04:24 PM.
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OK, now I'm thinking some more...very hard for me BTW...LOL !!...since this DTC is TAC module related along with the TPS, APP sensor, and TAC motor ALL are monitored by the TAC module "maybe" the PCM thinks the car is in "clear flood mode" which would inhibit injector pulse. The PCM would see high TPS voltages (when you do a clear flood crank) and inhibit injector pulse and then you'll have a no start...I can give you some voltages you SHOULDN'T see with KOEO so if you have a DVOM maybe you can check some of the sensor wiring...this is ONLY a S.W.A.G (scientific wild a$$ guess)...if you have a 12 volt test light it takes about 2 minutes to check injector pulse. And another thing a P1518 is also related TPS DTC's !!
Last edited by C5 Diag; Sep 25, 2018 at 06:00 PM.
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From: Newark NY
MMMM ??...we can try to attack this as maybe just a normal "cranking no start" for now...correct that it DOES CRANK ??...I think the C1278 is a steering DTC...can't remember...now reading your initial post you said you had a "long crank time" when starting....this "symptom" sometimes points to a crank sensor going bad...did you have a longer crank time again ???...if you want we can attack this as I had said...a cranking no start. Let me know !!
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From: Cape Coral, Florida
the code, and no start are connected to each other.... When there is no code the car starts fine. When the code appears. It will crank and crank and crank with no start. Usually leaving it alone for an undetermined amount of time will fix everything.... Currently another 2 days strong with no issues
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From: Newark NY
Back from the dead again... Or back to being dead again....
Car ran fine again all this time. Left work for home got 15 min down the road and car shut off without any warning at all (it has never done this) once it started it was always fine. Anyway i was able to pull even more codes,
P0102 p0443 p0801p0803 p1518 p1545
All came up as current the last two were also history. Googled them all, and its for all different issues (go figure) so im hoping maybe they are just ghost codes?
Either way a local mechanic is taking over from here.
Car ran fine again all this time. Left work for home got 15 min down the road and car shut off without any warning at all (it has never done this) once it started it was always fine. Anyway i was able to pull even more codes,
P0102 p0443 p0801p0803 p1518 p1545
All came up as current the last two were also history. Googled them all, and its for all different issues (go figure) so im hoping maybe they are just ghost codes?
Either way a local mechanic is taking over from here.
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From: Newark NY
like I said all this time i have NEVER seen any of these codes before aside from the 2 that are history, and after i cleared tbem, they didn't come back... I find it hard to believe all of these would fail all at one time. Hoping it's just ghost codes... Or possibly a bad PCM causing all of them as well? Im ok paying for it as long as iknow what the issue is. And that it's fixed
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From: Cape Coral, Florida
I doubt all these different codes would set all at once but if the tech clears all the codes and they come back I’d love to see how he diagnoses it !!...keep us advised !!
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From: Cape Coral, Florida
HOLY CRAP !!!...has your car been taking to mine ??...I was just about to pull my car out of my garage tonight to check a few things and I had a “low voltage” followed by active handling/ reduced power...left my key on while I hooked up my scan tool...checked all modules and had a PCM fault...was a P1518 !!...LOL !!...went to live data and had no TPS voltage response pushing the accelerator !!...started car...barely ran...shut down car cleared coded and ran OK on restart... should be a fun diag...haven’t had any issues with the car in years !!...wont be able to look at it till Monday !!
Last edited by C5 Diag; Oct 4, 2018 at 10:05 PM.